1. Field of the Invention
The present invention relates to an antenna structure in which an antenna is electrically connected to a circuit board when an antenna side attachment section is inserted into an antenna attachment hole provided in a case. Furthermore, this invention relates to the antenna structure wherein an outside antenna is switch-connected to the circuit board when a coaxial connector is inserted.
2. Description of the Related Art
One example of an antenna, which is secured by being projected to the outside of a case of a mobile telephone, is known as a snap-in antenna. The snap-in antenna is secured by being inserted into an antenna attachment hole provided in the case, whereby the base of the antenna electrically connects to a circuit board. One example of a structure of such an antenna will be briefly explained. An elastically deforming tongue-piece is provided parallel to the diameter of an antenna side attachment section with its insertion tip side as the free end. An outwardly projecting clip is provided at the free end of the tongue-piece. An antenna attachment hole is provided in the case and allows the clip to be inserted therein while the tongue-piece elastically deforms. A clip section restricts the movement of the clip in the extraction direction after the clip has clipped to the case in the inserted state. A conductive spring member provided on a circuit board in the case elastically contacts and electrically connects to a conductive metal fitting which the base of the antenna is electrically connected to.
When the mobile phone is used inside a vehicle, the connection is switched to an outside antenna provided on the outside of the vehicle in order to improve the quality of the communication. This is achieved by the following structure. The outside antenna connects to a male coaxial connector. A female coaxial connector is provided on the case and comprises a switching circuit which is switched when the male coaxial connector is inserted. The connection between the antenna secured to the case and the outside antenna secured outside the vehicle switches ON and OFF depending on whether the male coaxial connector is inserted.
In the conventional snap-in antenna described above, the signal transmission path of the conductive spring member, which electrically connects the conductive metal fitting of the antenna to the circuit board, is comparatively long, and the antenna effect of the conductive spring member has a considerable influence on the overall antenna characteristics. Using a conductive spring member having a coaxial structure would complicate the structure and is therefore impractical. For these reasons, it has been difficult to obtain the desired antenna characteristics.
The female coaxial connector comprises a switching circuit for switching between the antenna secured to the case and the outside antenna secured outside the vehicle. The female coaxial connector has considerable transmission loss, and its large mount area makes miniaturization difficult.
The present invention has been achieved in order to improve the above-described difficulties of the conventional technology.
It is an object of this invention to provide an antenna structure in which the signal transmission path from the antenna to the circuit board can be shortened.
It is a further object of this invention to provide an antenna structure in which it is possible to switch between an antenna secured to a case and an outside antenna secured outside a vehicle with low transmission loss.
To achieve the objects, the antenna structure of this invention comprises a case having an antenna attachment hole, which an attachment section of an antenna can be inserted into. A spring connector is provided on a circuit board inside the case and has a plunger. The plunger is elastically forced to protrude in a direction which intersects the insertion direction of antenna the attachment section into the case. A conductive member is provided to the attachment section of said antenna and electrically connects to the base of the antenna. When the attachment section is inserted into said antenna attachment hole while said conductive member is facing said plunger, the plunger elastically contacts the conductive member.
Further, the antenna structure of this invention comprises a conductive member which is electrically connected to the base of the antenna; a spring connector having a plunger which elastically contacts the conductive member and being provided on the circuit board provided in the case; a through-hole which is provided at the position on the conductive member which the plunger elastically contacts, the through-hole having a diameter which is narrower than the tip face of the plunger; a second spring connector which has a second plunger, one end of the second plunger passing through said through-hole and directly contacting the plunger and being elastically forced in the direction of its other end; and a coaxial connector containing section which is provided at the other end of the second plunger of the second spring connector and which a coaxial connector can be inserted into. A center conductor of the inserted coaxial connector forcibly moves the second plunger so that it directly contacts the plunger. The plunger resists the elasticity and is moved by a pressing force, thereby becoming separated from the conductive member.